In facilities concerned to radioactive substances, such as atomic power plants, facilities for experiments relating to atomic power, nuclear fuel handling facilities, fuel reprocessing plant and ships using atomic power as motive power, a large quantity of radioactive solid waste is produced. For disposal of incombustible radioactive solid waste among the radioactive solid waste, a method of solidifying the radioactive solid waste with cement, a method of compressing the radioactive solid waste, and a method of melting the radioactive solid waste at high temperatures and solidifying the molten waste, etc. are known.
Most of the incombustible radioactive solid waste contains metallic aluminum. For example, high efficiency particulate air filters for exhausted gas, which are so called "HEPA filers" and are used in the system for purifying air inside buildings such as atomic power plants, comprise a glass fiber filter and an aluminum spacer.
In the disposal method by heating and melting the radioactive solid waste containing aluminum, the aluminum is oxidized to thereby form an Al.sub.2 O.sub.3 layer on a surface of the sheet-like or massive radioactive solid waste. This layer is a protective layer, whereby the sheet-like or massive radioactive solid waste is not melted and remains unchanged as it is.
In the disposal method by solidifying the radioactive solid waste containing aluminum with hydraulic cement such as Portland cement, when the solid waste is mixed with the cement, calcium hydroxide in the cement reacts with aluminum to generate bubbles of a hydrogen gas, and setting of cement begins before generation of a hydrogen gas is completed. Therefore, no dense cement solid can be obtained, and the resulting cement solid has poor mechanical strength and insufficient properties of preventing oozing of radioactive nuclide.
For the disposal of the radioactive waste containing metallic aluminum by means of solidification, a method in which aluminum is previously reacted with an alkali substance or hydrogen peroxide to generate a hydrogen gas and thereby solidifying with cement has been proposed in, for example, Japanese Patent Laid-Open Publication No. 32000/1986 and No. 28700/1992. In the use of Portland cement hitherto applied, however, if the alkali concentration is too high, quick setting reaction takes place in the mixing process. As a result, operations for the solidification become impossible, or if possible, any cement solid having good solid properties (e.g., compression strength) cannot be obtained.
It has been also proposed that lithium nitrate is added to inhibit corrosion caused by the reaction of aluminum in the radioactive solid waste with cement. However, whether the inhibition effect exerted by the corrosion inhibitor continues over hundreds years has not been clarified.
Under such circumstances as described above, the present inventors have earnestly studied methods of disposal of radioactive solid waste containing aluminum, and as a result, we have found that disposal of the radioactive solid waste can be efficiently made by previously reacting the aluminum with an alkali substance to generate a hydrogen gas and then adding a solidifying material containing a latent hydraulic material as a main component to the reaction liquid to solidify the liquid. The present inventors have also found that the solid thus obtained has excellent mechanical strength and properties of preventing oozing of radioactive nuclide. Based on the finding, the present invention has been accomplished.